The invention is in the field of electronic reproduction technology and is directed to a method for the exposure of recording materials with a plurality of, for example, parallel light beams, preferably laser beams, whose brightness is controlled dependent on the information to be recorded.
In electronic reproduction technology, multi-beam exposure methods are utilized for the exposure of printing forms in order to achieve an adequately high exposure speed as well as an adequately high exposure intensity. For that purpose, a bundle of N parallel laser beams is moved relative to the recording material and N lines of the image data to be recorded are simultaneously exposed with every sweep. The printing forms can be exposed on film material, so what are referred to as color separation films arise, these subsequently serving for the production of printing plates with a photographic re-copying method. Instead, the printing plates themselves can be exposed in a multi-beam plate exposer or in a digital printing press. Finally, there is also the application of multi-beam exposure methods in order to produce flexo-printing forms or rotogravure forms by selective erosion of material with high-power laser beams. The recording material can be on a drum (drum exposer), in a cylindrical trough (inside drum exposer) or on a planar plate (flatbed exposer).
A number of optical arrangements and principles are known for generating parallel laser beams. For example, one laser beam is split into a plurality of individually modulated beams by means of an acousto-optical modulator. A plurality of laser beams can also be employed, each thereof being modulated with a separate acousto-optical modulator. Or a plurality of laser diodes arranged in a row are employed, these being individually modulated. A row of laser diodes can also be integrated in a laser diode chip. Alternatively, a broad light band in front of which a row of individually controllable light valves is arranged can be generated with one laser diode.
Independently of the application, i.e. what type of printing form is produced on what recording material, and independently of the mechanical and optical arrangement employed, there is the problem in all multi-beam exposure methods that, given outage of one of the parallel laser beams until the repair thereof, the exposure unit can either not be employed at all or a limited operation with the remaining, functional laser beams is only possible with an involved and complicated control unit.
It is therefore an object of the present invention to specify a method for the multi-beam exposure of recording materials with which the exposure arrangement can continue to be operated in a simple way and, thus, cost-beneficially, even given outage of one or more laser beams.
According to the present invention, a method is provided for multi-beam exposure of the printing form, such as with laser beams. The laser beams are subdivided into active and inactive laser beams. With a computer, printing form data are transmitted to a distributor via a data line as a sequence of recording lines. Recording lines of the printing form are transmitted via the data line for the active laser beams and empty lines are inserted into the transmitted sequence of the recording lines for the inactive laser beams. The distributor cyclically distributes the recording lines onto the input stages of an optics head wherein N parallel laser beams are generated and modulated with the printing form data of the recording lines.
The Prior Art and the inventive method are explained in greater detail below on the basis of FIGS. 1 through 4.